2,4-D Mineralization as Affected by Pre-Incubation Length of Amended Soils

2,4-D Mineralization as Affected by Pre-Incubation Length of Amended Soils
M. Reimer and A. Farenhorst; Department of Soil Science, University of Manitoba, Winnipeg, MB, Canada
Introduction
Objective
Conclusions
Since its introduction in the 1940’s, 2,4-D (2,4dichlorophenoxyacetic acid) has been a widely used broadleaf
herbicide. Soil microbes play a large role in the degradation
and mineralization of 2,4-D in soil. The addition of organic
amendments, such as livestock manure or municipal
biosolids, can affect the organic matter content, microbial
population and nutrient status of soil. These properties of
organic amendments may play an important part in
determining the fate of 2,4-D in soil.
The objective of this study was to determine whether increasing the
amount of time between applications of fresh hog manure or municipal
biosolids and 2,4-D application would result in a change in the total
mineralization of 2,4-D.
Longer incubation time decreased the total amount of 2,4-D
mineralization. Applying 2,4-D immediately following
amendment addition results in the greatest total 2,4-D
mineralization. 28 days of amendment pre-incubation resulted
in the lowest total mineralization.
This data has implications for producers who apply
amendments and pesticides within a narrow time frame. There
may be less risk of 2,4-D carryover and possible crop damage
when 2,4-D is applied immediately after amendment
application.
Figure 1. 2,4-D Molecule
Cl
Results
For both amendment treatments and the control soil, total 2,4-D
mineralization decreased with increasing pre-incubation time (Figure
3). Differences were greatest for the biosolid-amended soils, where
the total herbicide mineralization decreased from 47% (2,4-D
immediately applied) to 21% (2,4-D applied at 28 days following
amendment application). For manure-amended soil, total herbicide
mineralization decreased from 42% to 20%, while the differences in
mineralization were much smaller for the control soil.
The soil was incubated at 20oC for 0, 7, 14, or 28 days prior to
addition of 2,4-D, which was applied at a rate of 0.62 kg
active ingredient/ha as a mixture of
For applications of 2,4-D immediately following amendment
additions (Figure 3; 0 days), greatest total 2,4-D mineralization was
measured in biosolid-amended soils, intermediate in manured soils,
and lowest in control soils.
radio-labelled and analytical grade
2,4-D. Small vials containing 5 mL
of 0.5M NaOH were used to trap the
14CO as it evolved from the soil and
2
measured using liquid scintillation
counting.
Mineralization was
measured for 100 days after 2,4-D
addition and quantified as the amount
of 14CO2 evolved from the soil as a
percen-tage of the initial 14C 2,4-D
applied.
Figure 2. Soil microcosm
For more information, contact:
[email protected]
These differences were not as pronounced when 2,4-D was added 7,
14 or 28 days after amendment application. Mineralization was
greater in the biosolid-amended soil in the 7-day pre-incubation
treatment than in manured or control soils, but similar total
mineralization was measured in the biosolid- and manure-amended
soils in the 14 and 28-day pre-incubation lengths.
50
45
40
35
30
25
20
15
10
5
0
Manure
0 Days
7 Days
14 Days
Biosolid
Control
28 Days
Figure 3. 2,4-D Mineralization in amended soils preincubated for different lengths of time
The control soil reached greater total 2,4-D mineralization in the
14-day pre-incubation treatment than in amended soils, and
reached similar total mineralization in the 28-day treatment as the
amended soils. In fact, there is no significant effect of incubation
length on 2,4-D total mineralization in control soils.
255
2,4-D mineralization was measured in a Chernozemic sandy
loam soil collected near Macgregor, MB. Samples from the
top 10 cm of the soil profile were passed through a 2 mm
sieve. Microcosms were assembled using 500 ml mason jars
(Figure 2). 30 g of soil was placed in a small jar, to which 112
kg N/ha (as NH4+-N) of fresh hog manure and municipal
biosolids were added, or left untreated (control). Moisture
content of the soil was brought up to 70% field capacity.
% Mineralization
Methods and Materials
OCH2COOH
Cl